Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1 % (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2 % (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 μmol m^?2s^?1 for Chlorella sp. (22.5 %) and S. obliquus R8 (23.7 %) and 80 μmol m^?2s^?1 for C. vulgaris CCAP211/11B (20.1 %) and B. braunii FC124 (34.9 %).     

Productivity and biochemical composition of <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> and <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>: effects of different cultivation approaches

The present work evaluated biomass productivity, carbon dioxide fixation rate, and biochemical composition of two microalgal species, Phaeodactylum tricornutum (Bacillariophyta) and Tetradesmus obliquus (Chlorophyta), cultivated indoors in high-technology photobioreactors (HT-PBR) and outdoors both in pilot ponds and low-technology photobioreactors in a greenhouse in southern Italy. Microalgae were grown in standard media, under nitrogen starvation, and in two liquid digestates obtained from anaerobic digestion of agro-zootechnical and vegetable biomass. P. tricornutum, cultivated in semi-continuous mode in indoor HT-PBRs with standard medium, showed a biomass productivity of 21.0?±?2.3 g m^?2 d^?1. Applying nitrogen starvation, the lipid productivity increased from 2.3 up to 4.5?±?0.5 g m^?2 d^?1, with a 24 % decrease of biomass productivity. For T. obliquus, a biomass productivity of 9.1?±?0.9 g m^?2 d^?1 in indoor HT-PBR was obtained using standard medium. Applying liquid digestates as fertilizers in open ponds, T. obliquus gave a biomass productivity (10.8?±?2.0 g m^?2 d^?1) not statistically different from complete medium such as P. tricornutum (6.5?±?2.2 g m^?2 d^?1). The biochemical data showed that the fatty acid composition of the microalgal biomass was affected by the different cultivation conditions for both microalgae. In conclusion, it was found that the microalgal productivity in standard medium was about doubled in HT-PBR compared to open ponds for P. tricornutum and was about 20 % higher for T. obliquus.     

Lipid and total fatty acid productivity in photoautotrophic fresh water microalgae: screening studies towards biodiesel production

Microalgae are considered as a promising feedstock for biomass production. The selection of the most suitable species is based on several key parameters such as lipid and fatty acid productivity. In the present study, the growth of different microalgae strains was examined in freshwater media for photoautotrophs suited for large-scale applications to identify the most suitable medium for each species. In the optimal medium, Scenedesmus obliquus showed the highest biomass productivity measured as increase of cell dry weight (0.25 g cellu dry weight (CDW) L^?1 day^?1), while Botryococcus braunii showed the highest lipid and total fatty acid content (430 and 270 mg g^?1 CDW, respectively) among the tested species. Regarding lipid and total fatty acid productivity, S. obliquus was the most lipid and total fatty acid productive strain with 41 and 18 mg L^?1 day^?1 during the exponential phase, respectively. Additionally, the proportion of saturated and monounsaturated fatty acids increased with duration of the incubation in S. obliquus, while polyunsaturated fatty acids decreased. These results nominate S. obliquus as a promising microalga in order to serve as a feedstock for renewable energy production.     

Feeding efficiency of Chaoborus flavicans (Insecta, Diptera) under turbulent conditions

Turbulence can affect predator–prey interactions. The effect of turbulence on the feeding efficiency of an ambush predator was tested with laboratory experiments. The experiments were conducted in 100-L aquaria in which ten individuals of fourth instar Chaoborus flavicans larvae were placed as predators. Two prey densities (3 and 10 ind. of Daphnia pulex L^?1) and two durations (30 and 120 min) were tested in a nonturbulent treatment and five different turbulence levels [average root-mean-square (RMS) velocities ranging from 0 to 7.3 cm s^?1, corresponding dissipation rates from 7.2 × 10^?7 to 1.3 × 10^?3 m² s^?3]. We hypothesized that the feeding rate of C. flavicans would be enhanced by turbulence due to increasing encounter rates up to a turbulence level above which a disturbance in post-encounter processes would lead to reduced feeding efficiency. However, the results showed no significant increase in the feeding rate of C. flavicans at intermediate turbulence. At high turbulence we found the expected significant negative response in the feeding rate of Chaoborus larvae. The feeding rate declined below the rates at nonturbulent and intermediate turbulence conditions as the average RMS velocity exceeded 3.1 cm s^?1 (dissipation rate 9.9 × 10^?5 m² s^?3, respectively).     

Utilization of gaseous emissions from a methanol plant for cultivation of <Emphasis Type="Italic">Acutodesmus obliquus</Emphasis>

This study aimed to culture the green alga Acutodesmus obliquus utilizing the gaseous emissions containing a high concentration of CO₂ (99.13 %) from a methanol plant and study the tolerance of microalgae. The effect of CO₂ concentration, aeration rate, inoculum concentration, intermittent sparging, and nitrogen sources on the growth of A. obliquus was examined. Acutodesmus obliquus also was cultivated in a 500-L pilot outdoor tubular photobioreactor (OTP) to advance the laboratory scale system to outdoor scale-up applications. The results showed that A. obliquus could tolerate high CO₂ concentrations of 50 %, and a maximum biomass of 0.935 g L^?1 (dry weight) was achieved at 20 % CO₂. An aeration rate of 500 mL min^?1, inoculum concentration (optical density at 680 nm [OD₆₈₀]?=?0.3), and intermittent sparging of 10 min per 2 h enhanced growth to the optimum and influenced culture pH and photosynthesis. Urea as a nitrogen source was shown to be more beneficial to cell growth. A urea concentration of 0.3 g L^?1 and an N/P ratio of 15 led to maximum biomass accumulation thus enhancing the gaseous emission utilization efficiency. In conclusion, this work demonstrated that gaseous emissions containing high concentration of CO₂ from a methanol plant could be directly introduced into A. obliquus cultures and that A. obliquus was suitable well for large-scale outdoor cultivation in a tubular photobiorecator.     

An applicable nitrogen supply strategy for attached cultivation of Aucutodesmus obliquus

The “attached cultivation” method of microalgae in which the wet paste of algal biomass is attached onto supporting materials to form an immobilized biofilm layer, and the culture medium is supplied to this layer to provide nutrients and moisture for growth was highly efficient in biomass production and represents a promising technology to improve the biofuel industry. To optimize the nitrogen supply strategy for this attached cultivation method, the growth and total lipids accumulation properties for the green alga Aucutodesmus obliquus with this method were studied under different quantities of nitrogen source and different volumes of aqueous medium that continuously circulated inside the photobioreactor. Results showed that, compared with medium volume, the nitrogen quantity was a stronger factor affecting the growth and total lipid accumulation. An optimized nitrogen supply strategy for the attached cultivation of A. obliquus is proposed as circulating ca. 60 L of BG-11 medium containing 1/10 of nitrate concentration for 1 m² of cultivation surface. With this strategy, the attached A. obliquus accumulated biomass and total lipids simultaneously and obtained a high triacylglyceride productivity of 2.53 g m^?2 day^?1 in 7 days under subsaturated illumination of 100 μmol photons m^?2 s^?1. The water usage of 60 L m^?2 was potentially decreased to <2 L m^?2 if the nutrient supply was further improved. Dissolving the nitrogen source in small volume was the best way to efficiently utilize the nitrogen source with minimum of waste.     

Biomass, lipid content, and fatty acid composition of freshwater Chlamydomonas mexicana and Scenedesmus obliquus grown under salt stress

Two freshwater microalgae including Chlamydomonas mexicana and Scenedesmus obliquus were grown on Bold Basal Medium (BBM) with different levels of salinity up to 100 mM NaCl. The dry biomass and lipid content of microalgae were improved as the concentration of NaCl increased from 0 to 25 mM. Highest dry weight (0.8 and 0.65 g/L) and lipid content (37 and 34 %) of C. mexicana and S. obliquus, respectively, were obtained in BBM amended with 25 mM NaCl. The fatty acid composition of the investigated species was also improved by the increased NaCl concentration. At 50 mM, NaCl palmitic acid (35 %) and linoleic acid (41 %) were the dominant fatty acids in C. mexicana, while oleic acid (41 %) and α-linolenic acid (20 %) were the major fractions found in S. obliquus.     

Effect of high ferric ion concentrations on total lipids and lipid characteristics of Tetraselmis subcordiformis,Nannochloropsis oculata and Pavlova viridis

Microalgae as sources for biodiesel production have been widely investigated. Microalgae biomass, lipid content and fatty acid profiles of microalgae are limiting factors for the cost-effective production of biodiesel. In this paper, the effects of high ferric ion concentrations on three species of microalgae (Tetraselmis subcordiformis, Nannochloropsis oculata and Pavlova viridis) were studied. The microalgae were cultured in different concentrations (1.2?×?10^?2, 1.2?×?10^?1, 1.2 and 12 mmol L^?1) of ferric ion. The growth, lipid content and fatty acid profiles of the three microalgae were analysed. When algae were cultured in 1.2 mmol L^?1 ferric ion for 10 days, the final cell density and specific growth rates of T. subcordiformis, N. oculata and P. viridis decreased significantly (p?<?0.05), and the total lipid contents of the microalgae, 33.72, 37.34 and 29.48 % (dry mass) in T. subcordiformis, N. oculata and P. viridis, respectively, were higher than those at other concentrations. The neutral lipid/total lipid ratios of the three microalgae species increased with increasing ferric ion concentration. Neutral lipids accounted for 50.75, 48.37 and 46.59 % of the total lipid in T. subcordiformis, N. oculata and P. viridis, respectively, when cultured in 12 mmol L^?1 ferric ion. The proportions of saturated fatty acids in all three species cultured in 12 mmol L^?1 ferric ion were significantly higher than those cultured in lower ferric ion concentrations. An optimum ferric ion concentration can improve the properties of T. subcordiformis, N. oculata and P. viridis as sources for biodiesel.     

Sediment microstructure and resuspension behavior depend on each other

The critical shear stress of resuspension and rates of erosion for cohesive and loosely structured sediments must be obtained by direct measurements since there is no theoretical calculation. An in situ experiment on sediment resuspension was performed in a shallow lake (Langer See, NE Germany; area = 1.27 km², z_max = 3.8 m) in summer 2006 using a hydrodynamically calibrated erosion chamber (Ø 20 cm). Shear velocity (u*) was incrementally increased in 11 steps (0–2.19 cm s^?1) to initiate resuspension events. Entrainment rates (E) of suspended particulate matter (E_SPM), total P (E_TP), chlorophyll a (E_Chl a), and soluble reactive P (E_SRP) were determined by mass balance. Two subsequent critical u* (0.53 cm s^?1 and 1.48 cm s^?1) support the ‘two-layered bed’ model of a fluffy surface aggregate layer (freshly deposited phytodetritus prone to resuspension) and an underlying more consolidated biostabilised layer. Patterns in E_SPM (2–106 g m^?2 h^?1), E_TP (11–532 mg m^?2 h^?1), and E_Chl a (3–24 μg m^?2 h^?1) revealed a sediment surface maximum of TP and Chl a and their theoretical vertical logarithmic decrease within 4 mm sediment depth, the maximum thickness of sediment layer entrained. The advective E_SRP flux (17 mg m^?2 h^?1) was 43 times higher than the diffusive SRP flux (0.4 mg m^?2 h^?1). The TP and Chl a micro-profiles suggest that cohesive sediment bed formation is a function of both settling (fluff) and consolidation (biostabilisation). Thus, sediment microstructure and resuspension behavior depend on each other.     

Optimization of cultivation conditions for fatty acid composition and EPA production in the eustigmatophycean microalga Trachydiscus minutus

We determined the effects of cultivation conditions (nitrogen source, salinity, light intensity, temperature) on the composition of polyunsaturated fatty acids (PUFAs) and the production of eicosapentaenoic acid (EPA) in the laboratory cultured eustigmatophycean microalga, Trachydiscus minutus. T. minutus was capable of utilizing all nitrogen compounds tested (potassium nitrate, urea, ammonium nitrate, ammonium carbonate) with no differences in growth and only minor differences in fatty acid (FA) compositions. Ammonium carbonate was the least appropriate for lipid content and EPA production, while urea was as suitable as nitrates. Salinity (0.2 % NaCl) slightly stimulated EPA content and inhibited growth. Increasing salinity had a marked inhibitory effect on growth and PUFA composition; salinity at or above 0.8 % NaCl was lethal. Both light intensity and temperature had a distinct effect on growth and FA composition. The microalga grew best at light intensities of 470–1,070 μmol photons m^?2 s^?1 compared to 100 μmol photons m^?2 s^?1, and at 28 °C; sub-optimal temperatures (20, 33 °C) strongly inhibited growth. Saturated fatty acids increased with light intensity and temperature, whereas the reverse trend was found for PUFAs. Although the highest level of EPA (as a proportion of total FAs) was achieved at a light intensity of 100 μmol photons m^?2 s^?1 (51.1?± 2.8 %) and a temperature of 20 °C (50.9?±?0.8 %), the highest EPA productivity of about 30 mg L^?1?day^?1 was found in microalgae grown at higher light intensities, at 28 °C. Overall, for overproduction of EPA in microalgae, we propose that outdoor cultivation be used under conditions of a temperate climatic zone in summer, using urea as a nitrogen source.     

Screening Microalgae Strains for Biodiesel Production: Lipid Productivity and Estimation of Fuel Quality Based on Fatty Acids Profiles as Selective Criteria

The viability of algae-based biodiesel industry depends on the selection of adequate strains in regard to profitable yields and oil quality. This work aimed to bioprospecting and screening 12 microalgae strains by applying, as selective criteria, the volumetric lipid productivity and the fatty acid profiles, used for estimating the biodiesel fuel properties. Volumetric lipid productivity varied among strains from 22.61 to 204.91 mg l^?1 day^?1. The highest lipid yields were observed for Chlorella (204.91 mg l^?1 day¹) and Botryococcus strains (112.43 and 98.00 mg l^?1 day^?1 for Botryococcus braunii and Botryococcus terribilis, respectively). Cluster and principal components analysis analysis applied to fatty acid methyl esters (FAME) profiles discriminated three different microalgae groups according to their potential for biodiesel production. Kirchneriella lunaris, Ankistrodesmus fusiformis, Chlamydocapsa bacillus, and Ankistrodesmus falcatus showed the highest levels of polyunsaturated FAME, which incurs in the production of biodiesels with the lowest (42.47–50.52) cetane number (CN), the highest (101.33–136.97) iodine values (IV), and the lowest oxidation stability. The higher levels of saturated FAME in the oils of Chlamydomonas sp. and Scenedesmus obliquus indicated them as source of biodiesel with higher oxidation stability, higher CN (63.63–64.94), and lower IV (27.34–35.28). The third group, except for the Trebouxyophyceae strains that appeared in isolation, are composed by microalgae that generate biodiesel of intermediate values for CN, IV, and oxidation stability, related to their levels of saturated and monosaturated lipids. Thus, in this research, FAME profiling suggested that the best approach for generating a microalgae-biodiesel of top quality is by mixing the oils of distinct cell cultures.     

Absence of negative allelopathic effects of cylindrospermopsin and microcystin-LR on selected marine and freshwater phytoplankton species

Cyanobacterial toxins have been regarded by some researchers as allelopathic substances that could modulate the growth of competitors. Nevertheless, often the concentrations of toxins used are too high to be considered ecologically relevant. In this work we tested the hypothesis that microcystin-LR (MC-LR) and cylindrospermopsin (CYN) at ecologically relevant concentrations have no allelopathic effects on some species of phytoplankton. Extracts containing the toxins as well as pure MC-LR and CYN toxins were used to assess their effects on the growth rates of Nannochloropsis sp., Chlamydomonas reinhardtii, and Chlorella vulgaris. Cyanobacterial crude extracts induced more pronounced effects on growth rates than pure toxins. Microcystis aeruginosa and Aphanizomenon ovalisporum crude extracts containing MC-LR and CYN at 0.025–2.5 mg l^?1 stimulated growth rates of microalgae, whereas A. ovalisporum crude extracts containing 2.5 mg l^?1 of CYN strongly inhibited growth rates of microalgae after 4 and 7 days of exposure. MC-LR and CYN at environmentally occurring concentrations were unable to affect negatively the growth of microalgae, and therefore these molecules may play roles other than allelopathy in natural ecosystems.     

Current velocity influences the facilitation and removal of algae by stream grazers

The modification of flows in lotic ecosystems can have dramatic effects on abiotic and biotic processes and change the structure of basal trophic levels. In high-gradient streams, most of the biota are benthic, and decreased flow may homogenize and reduce benthic current velocity, potentially changing stream ecosystem function. Grazing by macroinvertebrates is an important component of stream function because grazers regulate energy flow from primary producers to higher trophic levels. We conducted an experiment to examine how macroinvertebrate grazers facilitated or removed algal biomass across a gradient of benthic current velocity (0–40 cm s^?1). We chose three grazers (Drunella coloradensis, Cinygmula spp., and Epeorus deceptivus) from a montane stream and conducted our experiment using 24 artificial stream channels that had three treatments: no grazers (control), single-grazer, and combined-grazer treatments. In the absence of grazers, algal biomass increased with benthic current velocity. Grazer treatments differed from the control in that more algal biomass was removed at higher velocities, whereas algal accrual was largely facilitated at low velocities. The transition from facilitation to removal ranged from 4.5 to 5.9 cm s^?1 for individual grazer treatments and occurred at 11.7 cm s^?1 for the combined-grazer treatment. Our data suggest that velocity plays a significant role in the facilitation and removal of algae by macroinvertebrate grazers. Additionally, the patterns revealed here could have general implications for algal accrual in systems where flow is reduced.     

Microalgae-mediated brewery wastewater treatment: effect of dilution rate on nutrient removal rates,biomass biochemical composition,and cell physiology

Microalgae have been used to remove nitrogen, phosphorus, and chemical oxygen demand (COD) from brewery wastewater (BWW). The microalga Scenedesmus obliquus was grown on BWW, using bubble column photobioreactors that operated under batch and continuous regimes. For the first time, the cell physiological status cell membrane integrity and enzymatic activity was monitored during the microalgae based BWW treatment, using flow cytometry. All the cultivations batch and continuous displayed a proportion of cells with intact membrane >?87%, although the continuous cultivations displayed a lower proportion of cells with enzymatic activity (20–40%) than the batch cultivations (97%). The dilution rate of 0.26 day^?1 was the most favorable condition, since the microalgae cultivation attained the maximum biomass productivity (0.2 g ash-free dry weight day^?1) and the total nitrogen and COD removal rates were the highest (97 and 74%, respectively), while the phosphorous removal rate was the third (23%).     

Bioflocculant produced by Chlamydomonas reinhardtii

Bioflocculants of Chlamydomonas reinhardtii were investigated under axenic conditions. C. reinhardtii was found to produce significant amounts of bioflocculants. Flocculating activity by C. reinhardtii began in the linear phase of growth and continued until the end of the stationary phase. The highest flocculating efficiency of the culture broth was 97.06%. The purified C. reinhardtii bioflocculant was composed of 42.1% (w/w) proteins, 48.3% carbohydrates, 8.7% lipids, and 0.01% nucleic acid. The optimum condition for bioflocculant production of C. reinhardtii was as follows: under temperature of 15°C to 25°C, pH 6–10 and illumination of 40–60 μmol photons m^?2 s^?1. The bioflocculants produced by C. reinhardtii showed maximum activity in pH ranges from 2 to 10. The flocculating activity was significantly enhanced by the addition of CaCl₂ as a co-flocculant at an optimal concentration of 4.5 mM.     

Growth kinetics and fucoxanthin production of <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> and <Emphasis Type="Italic">Isochrysis galbana</Emphasis> cultures at different light and agitation conditions

Fucoxanthin is a carotenoid that exerts multiple beneficial effects on human health. However, reports comparing microalgae culture conditions and their effect on growth and fucoxanthin production are still limited. Isochrysis galbana and Phaeodactylum tricornutum cultures in different light (62.0, 25.9, 13.5, or 9.1 μmol photons m^-2 s^-1), mixing conditions (1 vvm aeration or 130 rpm agitation), and media compositions (F/2 and Conway medium) were studied for comparison of cellular growth and fucoxanthin production on F/2 medium. I. galbana showed a better adaptation to tested culture conditions in comparison with P. tricornutum, reaching 2.15?×?10⁷?±?4.07?×?10⁶ cells mL^-1 and a specific growth rate (μ) of 1.12?±?0.05 day^-1 under aerated conditions and 62.0 μmol photons m^-2 s^-1 light intensity. Fucoxanthin concentration was about 25 % higher in P. tricornutum cultures under 13.5 μmol photons m^-2 s^-1 light intensity and aerated conditions, but the highest fucoxanthin total production was higher in I. galbana, where 3.32 mg can be obtained from 1 L batch cultures at the 16th day under these conditions. Moreover, higher cell densities (~32.41 %), fucoxanthin concentration (~42.46 %), and total production (~50.68 %) were observed in I. galbana cultures grown in Conway medium, if compared with cultures grown in F/2 medium. The results show that the best growth conditions did not result in the best fucoxanthin production for either microalgae, implying that there is not a direct relationship between cellular growth and fucoxanthin production. Moreover, the results suggest that I. galbana cultures on Conway medium are strong candidates for fucoxanthin production, where 1.2 to 15 times higher fucoxanthin concentration are observed in comparison to macroalgal sources.     

Carbon Dioxide and Methane Fluxes From Tree Stems,Coarse Woody Debris,and Soils in an Upland Temperate Forest

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m^?2 s^?1, mean ± 1 SD) and net sinks of CH₄ (?2.17 ± 1.60 nmol m^?2 s^?1). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m^?2 s^?1) and net CH₄ sink, but with large uncertainty (?0.27 ± 1.04 nmol m^?2 s^?1) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m^?2 s^?1), but also net CH₄ sources (up to 0.98 nmol m^?2 s^?1), with a mean of 0.11 ± 0.21 nmol m^?2 s^?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.     

Ecosystem respiration derived from 222Rn measurements on Rishiri Island, Japan

We evaluated the nighttime CO₂ flux (ecosystem respiration) on Rishiri Island, located at the northern tip of Hokkaido, Japan, from 2009 to 2011, by using the relationship between atmospheric ²²²Rn and CO₂ concentrations. The annual mean CO₂ flux was 1.8 μmol m^?2 s^?1, with a maximum monthly mean in July (4.6 ± 2.6 μmol m^?2 s^?1) and a broad minimum from December to March (0.33 ± 0.29 μmol m^?2 s^?1). The annual mean was comparable to fluxes at the JapanFlux sites in northern Japan. During the season of snow cover (mid-December to early April), the CO₂ flux was low (0.45 ± 0.43 μmol m^?2 s^?1). Total annual respiration was estimated at 679 ± 174 g cm^?2, about 8 % of which occurred during the season of snow cover.     

Effects of nitrogen supplementation of the culture medium on the growth, total lipid content and fatty acid profiles of three microalgae (Tetraselmis subcordiformis, Nannochloropsis oculata and Pavlova viridis)

To improve the properties of microalgae as sources for biodiesel production, three microalgae (Tetraselmis subcordiformis SHOU-S05, Nannochloropsis oculata SHOU-S14 and Pavlova viridis SHOU-S16) were cultured in media supplemented with different amounts of nitrogen (0, 0.22, 0.44, 0.88 and 1.76 mmol N·L^?1). The growth, total lipid contents, lipid classes and fatty acid profiles of the three microalgae were assayed after 10 days of cultivation. The results indicated that the specific growth rates of T. subcordiformis, N. oculata and P. viridis were lowest (0.014, 0.033 and 0.018, respectively) in the treatments without nitrogen supplementation and increased significantly with increasing nitrogen supplementation. The microalgae treated with 0.22 mmol N·L^?1 had the highest total lipid contents, which were 29.77, 35.85 and 32.10 % in T. subcordiformis, N. oculata and P. viridis, respectively. The total lipid contents as well as the proportions of neutral lipid in the three microalgae decreased significantly with increasing nitrogen supplementation between 0.22 and 1.76 mmol N·L^?1. The fatty acid profiles of the three microalgae were significantly different. The obvious characteristic of the fatty acid profile of T. subcordiformis was a high amount (17.68–22.22 %) of 18:3n3. However, EPA (C20:5n3) and C16 fatty acids were significantly high in N. oculata and P. viridis, respectively. N. oculata and P. viridis accumulated more 16-carbon fatty acids and fewer polyunsaturated fatty acids in nitrogen-limited media. It is therefore suggested that a limited nitrogen treatment is effective for improving the properties of P. viridis and N. oculata as sources for biodiesel.     

Cloning, Expression, and Enzymatic Characterization of Isocitrate Dehydrogenase from Helicobacter pylori

Isocitrate dehydrogenase (IDH) catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate with NAD(P) as a cofactor in the tricarboxylic acid cycle. As a housekeeping protein in Helicobacter pylori, IDH was considered as a possible candidate for serological diagnostics and detection. Here, we identified a new icd gene encoding IDH from H. pylori strain SS1. The recombinant H. pylori isocitrate dehydrogenase (HpIDH) was cloned, expressed, and purified in E. coli system. The enzymatic characterization of HpIDH demonstrates its activity with k _cat of 87 s^?1, K _m of 124 μM and k _cat/K _m of 7 × 10⁵ M^?1s^?1 toward isocitrate, k _cat of 80 s^?1, K _m of 176 μM and k _cat/K _m of 4.5 × 10⁵ M^?1s^?1 toward NADP. The optimum pH of the enzyme activity is around 9.0, and the optimum temperature is around 50 °C. This current work is expected to help better understand the features of HpIDH and provide useful information for H. pylori serological diagnostics and detection.